Happy faces/sad faces

This is the experimental set-up used to test whether dogs can discriminate emotional expressions of human faces. Photo by Anjuli Barber, Messerli Research Institute

Dogs can tell the difference between happy and angry human faces, according to a research published recently in the journal Cell Biology.

The discovery represents the first solid evidence that an animal other than humans can discriminate between emotional expressions in another species, the researchers say.

Previous attempts had been made to test whether dogs could discriminate between human emotional expressions, but none of them had been completely convincing. In the new study, the researchers trained dogs to discriminate between images of the same person making either a happy or an angry face. In every case, the dogs were shown only the upper or the lower half of the face. After training on 15 picture pairs, the dogs’ discriminatory abilities were tested in four types of trials, including (1) the same half of the faces as in the training but of novel faces, (2) the other half of the faces used in training, (3) the other half of novel faces, and (4) the left half of the faces used in training.

The dogs were able to select the angry or happy face more often than would be expected by random chance in every case, the study found. The findings show that not only could the dogs learn to identify facial expressions, but they were also able to transfer what they learned in training to new cues.

“Our study demonstrates that dogs can distinguish angry and happy expressions in humans, they can tell that these two expressions have different meanings, and they can do this not only for people they know well, but even for faces they have never seen before,” says Ludwig Huber, senior author and head of the group at the University of Veterinary Medicine Vienna’s Messerli Research Institute.

This research adds to the body of knowledge about the human-animal bond. The researchers believe it is likely that the dogs associate a smile with a positive meaning and an angry expression with a negative one.